Hard disk drives include at least one read-write head embedded in a slider and positioned near a rotating disk surface to access data organized as tracks on a rotating disk surface. Typically, the tracks are concentrically arranged on the rotating disk surface. The read-write head is positioned near the track by a voice coil actuator, which moves the slider through an actuator arm. The voice coil actuator includes a voice coil, which is stimulated by a time varying electrical signal from a servo controller. The time varying signal causes the voice coil to interact with fixed magnets, and pivot the actuator assembly it is coupled with, moving the actuator arm, and positioning the read-write head.
Often a hard disk drive has multiple read-write heads, accessing multiple rotating disk surfaces. Often a hard disk drive may include more than one disk. Each disk can support up to two disk surfaces for data storage.
There are typically two separate operations required to position the read-write head to access a track. First, a track seek operation is performed. This brings the read-write head close to the track. Then a track following operation is performed while the read-write head actively accesses the data. While following the track, a Position Error Signal (PES) is actively sensed by the interface circuitry coupled with the read channel of the read-write head. The PES is a distance measure derived from an encoded pattern laid down on the disk surface before the track data is actually written. The following of the track uses the PES signal to estimate distance from the written track, and adjust the voice coil stimulus, and possibly also control a micro-actuator coupled to the slider, to refine the positioning of the read-write head and optimize the reliability of the access operation being performed. TMR is usually measured as the acceptable amount of positional error for the read-write head on the servo track pattern.
The manufacturers of hard disk drives are constantly challenged to increase track density, to put more information onto each rotating disk surface of the hard disk drive. This has made the acceptable level of PES smaller and smaller. Recently, the TMR has become less than 10 nano-meters (nm).
Vibration of the disks and vibration of the head stack assembly containing the sliders are often considered today to be the most significant contributors to the PES errors of the track following operation. And airflow near the head stack assembly, particularly turbulent airflow, significantly contributes to vibration of the head stack assembly.
In the last few years, the use of disk dampers has become common. These devices narrow the gap between the rotating disk surfaces and the nearest stationary walls, affecting the air flowing in the gap to minimize the airflow turbulence near the head stack assembly. There are however problems with existing devices. The existing devices do not provide consistent dampening of air flow turbulence, in particular, there is a tendency for increased turbulence when the head stack assembly is near the inside diameter of the rotating disk surfaces. What is needed is a disk damper which consistently dampens air turbulence for a head stack assembly when position anywhere from the inside diameter to the outside diameter.